To dissipate heat generated from heat-generating bodies, such as semiconductor elements and machine parts, heat-dissipating bodies, such as heat sinks, are used. For the purpose of efficiently conducting heat, thermally conductive greases can be applied between heat-generating bodies and heat-dissipating bodies.
Thermally conductive greases have lower thermal conductivity than those of heat-generating bodies and heat-dissipating bodies (typically composed of metals) and thus are advantageously applied in the form of thinner films. In order not to form an air layer, which has significantly low thermal conductivity, between heat-generating bodies and heat-dissipating bodies, low-viscosity, high-fluidity thermally conductive greases are advantageous. For these reasons, in the case where gaps between heat-generating bodies and heat-dissipating bodies are narrow, low-viscosity thermally conductive greases have been suitably used.
In recent years, however, elements that generate heat have been increasing, and the total amount of heat generated have been prone to increase. Thus, heat is preferably dissipated from a plurality of electronic elements or from the entire substrate, rather than a specific electronic element. In these circumstances, various structures are used to dissipate heat. For example, heat-dissipating bodies can be mounted on different-height electronic elements, from which heat is to be dissipated and on heat-generating bodies arranged obliquely or transversely.
When an attempt is made to use a conventional thermally conductive grease in order to meet such demands, the grease cannot maintain an applied state and disadvantageously flows out because of its low viscosity. Thus, a thermally conductive grease with higher thixotropic properties has been developed and described in, for example, Japanese Unexamined Patent Application Publication No. 2011-088953 (Patent Literature 1).
In the case where a gap between a heat-generating body and a heat-dissipating body is wide, a heat-dissipating sheet as described in, for example, Japanese Unexamined Patent Application Publication No. 2006-332126 (Patent Literature 2) is conceivably used. Examples of the use of such a heat-dissipating sheet include the use of heat-dissipating sheets corresponding to different-height heat-generating bodies; the use of a soft heat-dissipating sheet; and the use of a heat-dissipating sheet with a hole corresponding to a portion of the heat-dissipating sheet to be brought into contact with a heat-generating body with large height.